https://neon.kde.org/faq
Neon is intentionally bound to LTS releases of Ubuntu with the intent to provide up-to-date KDE software on top of a stable base that you don't have to upgrade every 6 months. If you want to upgrade your whole system every 6 months then just stick with Kubuntu (with backports), which provides up-to-date KDE software within the support lifespan of each Ubuntu release.

With regards to the desktop, I would expect up-to-date Neon (on current LTS) and up-to-date Kubuntu (on latest Ubuntu release) to be very similar aside from minor branding differences (though there might be some more polish in Neon due to the amount of attention it's been receiving since it was created).

airdrik wrote:With regards to the desktop, I would expect up-to-date Neon (on current LTS) and up-to-date Kubuntu (on latest Ubuntu release) to be very similar aside from minor branding differences ...

This statement is not correct. The current Kubuntu release (17.04) has one-year(!!!) old outdated kdepim and all related libraries (16.04.3), which possess severely restricted functionality, particularly it does not support such crucial Plasma feature as PIM events in the Calendar widget (while all other Applications are 16.12.3) . And it seems, that today's snapshot of currently developed Kubuntu 17.10 also has the same shameful kdepim 16.04.3. ( Moreover, the current kdepim in staging ppa (ppa:kubuntu-ppa/staging-kdeapplications) for both Zesty and Artful are incomplete and not installable yet. So, all all currently available Kubuntu versions did not even approach to functionality of Neon user edition and are worth to be just skipped.

In Neon all works fine and currently the Neon itself and the Maui based on it are the only Ubuntu-based distributions with Plasma, which are worth to be used.

Hmm. That sounds like a rather disappointing level of neglect on the part of the Kubuntu devs; though I suppose it may be expected since iirc a number of them including their lead did leave Kubuntu to set up Neon.